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27 Mar 2006

Volume 88, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 133105 (2006); http://dx.doi.org/10.1063/1.2189203 (3 pages)

Premila Mohan, Junichi Motohisa, and Takashi Fukui
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Microphotoluminescence of exciton and biexciton around 1.5 μm from a single InAs/InP(001) quantum dot

G. Saint-Girons, N. Chauvin, A. Michon, G. Patriarche, G. Beaudoin, G. Brémond, C. Bru-Chevallier, and I. Sagnes

Appl. Phys. Lett. 88, 133101 (2006); http://dx.doi.org/10.1063/1.2185008 (3 pages) | Cited 10 times

Online Publication Date: 27 March 2006

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We report on the fabrication by low-pressure metalorganic vapor phase epitaxy of InAs/InP(001) quantum dots (QDs) emitting around 1.5 μm, and on the observation of microphotoluminescence (μPL) from a single QD in this wavelength range. The QDs are diamond shaped, with a density of 6.3∙109 cm−2. μPL experiments were carried out on a QD sample covered with a gold mask containing apertures (diameter of 200 nm). Well defined peaks corresponding to the emission of single QDs were recorded between 1.24 and 1.6 μm. The analysis of the pump power dependence of their intensity allows us to discriminate between exciton and biexciton emission lines.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Invasive growth of Co on (math×2math)R45° reconstructed O/Cu(001)

Xiangdong Liu, Takushi Iimori, Kan Nakatsuji, and Fumio Komori

Appl. Phys. Lett. 88, 133102 (2006); http://dx.doi.org/10.1063/1.2189190 (3 pages) | Cited 10 times

Online Publication Date: 27 March 2006

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Submonolayer growth of Co on the reconstructed Cu(001)(math×2math)R45°–O surface has been investigated by scanning tunneling microscopy. Cu atoms are displaced from the Cu(001)(math×2math)R45°–O structure by incoming Co atoms and subsequently aggregate into elongated islands. The deposited Co atoms are randomly distributed in the oxygen adsorbed surface as individual atoms and clusters at low coverages [ ⩽ 0.4 monolayers (ML)]. For larger coverages ( ≥ 0.5 ML), compact fcc Co patches are formed. The adsorbed oxygen acts as a surfactant. Interfacial intermixing is reduced when Co is deposited on the Cu(001)(math×2math)R45°–O surface.
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68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
68.43.Fg Adsorbate structure (binding sites, geometry)
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.35.Fx Diffusion; interface formation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.43.Mn Adsorption kinetics

Atomically resolved dynamic force microscopy operating at 4.7 MHz

Shigeki Kawai and Hideki Kawakatsu

Appl. Phys. Lett. 88, 133103 (2006); http://dx.doi.org/10.1063/1.2189193 (3 pages) | Cited 18 times

Online Publication Date: 27 March 2006

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We demonstrate atomically resolved frequency modulation dynamic force microscopy operating at 4.7 MHz using the third flexural mode of a silicon cantilever. A high spring constant due to the higher mode realized stable imaging with an amplitude of 2 Å, which was calculated to be a favorable value for high-resolution imaging. Although excessive stiffness decreases the sensitivity of the detection, a stable imaging was realized with a low noise heterodyne laser Doppler interferometer and a narrow bandwidth feedback circuit. An atomically resolved constant frequency shift images of the Si(111)-7×7 were obtained with the exposed and terminated dangling bonds at the tip apex.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
07.60.Ly Interferometers
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces

Comparison of structural and optical properties of InAs quantum dots grown by migration-enhanced molecular-beam epitaxy and conventional molecular-beam epitaxy

N. K. Cho, S. P. Ryu, J. D. Song, W. J. Choi, J. I. Lee, and Heonsu Jeon

Appl. Phys. Lett. 88, 133104 (2006); http://dx.doi.org/10.1063/1.2189195 (3 pages) | Cited 26 times

Online Publication Date: 27 March 2006

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We strongly support Guryanov’s speculation—that a thinner wetting layer is expected with quantum dots (QDs) grown by migration-enhanced epitaxy—with structural and optical measurements. InAs QDs grown by migration-enhanced molecular-beam epitaxy showed a larger size, lower density, ∼ 40% enhanced uniformity, ∼ 2 times larger aspect ratio, and a measurement temperature insensitivity of the photoluminescence linewidth compared to QDs grown by conventional molecular-beam epitaxy. The thickness of the wetting layer for the migration-enhanced epitaxial InAs QD (2.1 nm) was thinner than that of the counterpart (4.0 nm).
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.08.Bc Wetting

Fabrication of InP/InAs/InP core-multishell heterostructure nanowires by selective area metalorganic vapor phase epitaxy

Premila Mohan, Junichi Motohisa, and Takashi Fukui

Appl. Phys. Lett. 88, 133105 (2006); http://dx.doi.org/10.1063/1.2189203 (3 pages) | Cited 54 times

Online Publication Date: 27 March 2006

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We report the growth of InP/InAs/InP core-multishell nanowire arrays by selective area metalorganic vapor phase epitaxy. The core-multishell nanowires were designed to accommodate a strained InAs quantum well layer in a higher band gap InP nanowire. The precise control over nanowire growth direction and heterojunction formation enabled the successful fabrication of the nanostructure in which all three layers were epitaxially grown without the assistance of any catalyst. The grown nanowires were highly uniform, vertically oriented, and periodically aligned with controllable dimensions. 4 K photoluminescence measurements confirmed the formation of strained InAs quantum well on InP (110) sidewalls and the well widths corresponding to the photoluminescence peaks were in good agreement with calculated values.
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81.07.Vb Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.67.Lt Quantum wires
78.55.Cr III-V semiconductors

Thermoelectric effect in very thin film Pt/Au thermocouples

M. C. Salvadori, A. R. Vaz, F. S. Teixeira, M. Cattani, and I. G. Brown

Appl. Phys. Lett. 88, 133106 (2006); http://dx.doi.org/10.1063/1.2189192 (3 pages) | Cited 11 times

Online Publication Date: 28 March 2006

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The thickness dependence of the thermoelectric power of Pt films of variable thicknesses on a reference Au film has been determined for the case when the Pt film thickness, t, is not large compared to the charge-carrier mean free path. Pt film thicknesses down to 2.2 nm were investigated. We find that ΔSF = SB−SF (where SB and SF are the thermopowers of the Pt bulk and film, respectively) does not vary linearly as 1/t is the case for thin film thermocouples when the film thickness is large compared to the charge-carrier mean free path.
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72.15.Jf Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.At Metal and metallic alloys
07.20.-n Thermal instruments and apparatus

Geometrical enhancement of field emission of individual nanotubes studied by in situ transmission electron microscopy

Zhi Xu, X. D. Bai, and E. G. Wang

Appl. Phys. Lett. 88, 133107 (2006); http://dx.doi.org/10.1063/1.2188389 (3 pages) | Cited 36 times

Online Publication Date: 28 March 2006

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Field emission of an individual multiwalled carbon nanotube, driven by a customer-built piezomanipulator, was measured in a transmission electron microscope. The measurement geometry and the nanotube structure were imaged in situ. A linear dependence of field enhancement factor β on the distance d between the nanotube tip and its counteranode is found. The enhanced field emission mechanism is studied by a tip-flat emission model. The results indicate that the radius of emission apex r is an important factor in field emission with a relationship of β∝r−1/2, while the tube length has little influence on β.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Fg Nanotubes
68.37.Lp Transmission electron microscopy (TEM)

Implementation of submicrometric periodic surface structures toward improvement of organic-solar-cell performances

C. Cocoyer, L. Rocha, L. Sicot, B. Geffroy, R. de Bettignies, C. Sentein, C. Fiorini-Debuisschert, and P. Raimond

Appl. Phys. Lett. 88, 133108 (2006); http://dx.doi.org/10.1063/1.2188600 (3 pages) | Cited 30 times

Online Publication Date: 28 March 2006

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Submicrometric periodic patterning of an organic solar cell surface is investigated in order to optimize the photovoltaic conversion efficiency of the device. Patterning is achieved using a single-step all-optical technique based on photoinduced mass transport in azopolymer films. The polymer film with a structured surface is used as a substrate for an organic solar cell based on a copper phthalocyanine/C60 heterojunction. The effect of periodic patterning is investigated through the solar-cell optical-absorption properties and external quantum efficiency measurements. The possibility to increase the short circuit current density and the corresponding photovoltaic conversion efficiency is evidenced with one-dimensional periodic structures.
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84.60.Jt Photoelectric conversion
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Mn Polymer surfaces
85.60.-q Optoelectronic devices
61.41.+e Polymers, elastomers, and plastics

Synthesis and electronic properties of ZnO/CoZnO core-shell nanowires

Song Han, Daihua Zhang, and Chongwu Zhou

Appl. Phys. Lett. 88, 133109 (2006); http://dx.doi.org/10.1063/1.2187435 (3 pages) | Cited 12 times

Online Publication Date: 29 March 2006

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ZnO/CoZnO core-shell nanowires have been synthesized by depositing an epitaxial layer of CoxZn1−xO (x = 0.05−0.25) onto single-crystalline ZnO nanowires via pulsed-laser deposition. Detailed material analysis confirmed the core-shell structure and revealed a homogeneous distribution of Co atoms in the ZnO lattice. Field-effect transistors have been fabricated based on individual ZnO/CoZnO nanowires. These devices exhibited n-type transistor characteristics and intriguing magnetoresistance below 30 K.
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73.63.Nm Quantum wires
73.21.Hb Quantum wires
81.07.Vb Quantum wires
81.05.Dz II-VI semiconductors
85.30.Tv Field effect devices
75.50.Pp Magnetic semiconductors

Modeling the melting of supported clusters

Feng Ding, Arne Rosén, Stefano Curtarolo, and Kim Bolton

Appl. Phys. Lett. 88, 133110 (2006); http://dx.doi.org/10.1063/1.2187950 (3 pages) | Cited 42 times

Online Publication Date: 29 March 2006

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Molecular dynamics simulations have been used to study the structural and dynamic changes during melting of free and supported iron clusters ranging from 150 to 10 000 atoms. The results reveal a method for determining effective diameters of supported metal clusters, so that the melting point dependence on cluster size can be predicted in a physically meaningful way by the same analytic model used for free clusters.
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64.70.D- Solid-liquid transitions
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Theoretical investigation on photoconductivity of single intrinsic carbon nanotubes

Jing Guo, Muhammad A. Alam, and Youngki Yoon

Appl. Phys. Lett. 88, 133111 (2006); http://dx.doi.org/10.1063/1.2189827 (3 pages) | Cited 9 times

Online Publication Date: 29 March 2006

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The photoconductivity of carbon nanotube (CNT) Schottky barrier transistors is studied by solving the nonequilibrium Green’s function transport equation. The model provides a detailed and coherent picture of electron-photon coupling and quantum transport effects. The photocurrent shows peaks at photon energies near the subband gaps, which can be engineered by controlling the CNT diameter. Electron-phonon coupling (i) slightly broadens the peaks, (ii) leads to phonon-assisted photocurrent at certain energy ranges, and (iii) changes the energy-resolved photocurrent. We also show that the metal-CNT barrier height has a much smaller effect on the photocurrent than on the dark current.
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85.35.Kt Nanotube devices
85.60.Dw Photodiodes; phototransistors; photoresistors

Directed movement of Au–Si droplets towards buried dislocation networks on silicon bicrystals

C. H. Liu, W. W. Wu, and L. J. Chen

Appl. Phys. Lett. 88, 133112 (2006); http://dx.doi.org/10.1063/1.2189907 (3 pages) | Cited 9 times

Online Publication Date: 29 March 2006

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Directed movement of Au–Si alloy droplets towards buried dislocation grids on a Si bicrystal has been observed by in situ ultrahigh vacuum transmission electron microscopy. It was found that once the underlying dislocation structure was dissolved, the movement of Au–Si droplets was directed to the region with remaining dislocation network. The migration of Au–Si droplets is driven by the energy difference between the strained bicrystal and nonstrained single-crystal silicon. The directed movement by the buried dislocation network is potentially significant in a wide range of technologies.
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47.55.dr Interactions with surfaces
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.47.Fg Semiconductor surfaces

Deep ultraviolet photoluminescence studies of AlN photonic crystals

N. Nepal, J. Shakya, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 88, 133113 (2006); http://dx.doi.org/10.1063/1.2190452 (3 pages) | Cited 1 time

Online Publication Date: 29 March 2006

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Two-dimensional AlN photonic crystals (PCs) with varying periodicity/diameter down to 150/75 nm were fabricated. Deep ultraviolet photoluminescence spectroscopy has been employed to study the optical properties of AlN PCs. With PC formation, a 20-fold enhancement in the band edge emission intensity at 208 nm over unpatterned AlN epilayer has been observed. The emission intensity increases with decreasing lattice constant of AlN PCs. However, the spectral peak energy decreases with decreasing lattice constant, indicating a possible release of compressive stresses as a result of PC formation. Successful fabrication of AlN PCs opens up new opportunities for exploring novel physical phenomena in the artificially structured photonic band gap material system and their applications, particularly in the area of deep UV photonics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
42.70.Qs Photonic bandgap materials

Simple fabrication of a ZnO nanowire photodetector with a fast photoresponse time

J. B. K. Law and J. T. L. Thong

Appl. Phys. Lett. 88, 133114 (2006); http://dx.doi.org/10.1063/1.2190459 (3 pages) | Cited 92 times

Online Publication Date: 29 March 2006

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A zinc oxide (ZnO) nanowire photodetector was fabricated by a simple method of growing ZnO nanowires bridging the gap of two patterned zinc electrodes. The nanowire growth is self-catalytic, involving the direct heating of patterned Zn electrodes at 700 °C in an O2/Ar gas flow of 20 SCCM (standard cubic centimeter per minute at STP)/80 SCCM, respectively, at atmospheric pressure for 3 h. The fabricated photodetector demonstrated fast response of shorter than 0.4 ms to UV illumination in air, which could be attributed to the adsorption, desorption, and diffusion of water molecules in the air onto the nanowire significantly influencing the photoresponse.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
68.65.La Quantum wires (patterned in quantum wells)
81.16.Hc Catalytic methods
68.43.Mn Adsorption kinetics
66.30.J- Diffusion of impurities

Modulated optical transmission of subwavelength hole arrays in metal-VO2 films

J. Y. Suh, E. U. Donev, R. Lopez, L. C. Feldman, and R. F. Haglund

Appl. Phys. Lett. 88, 133115 (2006); http://dx.doi.org/10.1063/1.2190463 (3 pages) | Cited 19 times

Online Publication Date: 29 March 2006

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We demonstrate the modulation of the transmission of near-infrared light through a periodic array of subwavelength apertures in Ag–VO2 and Au–VO2 double-layer films using the semiconductor-to-metal phase transition in VO2. The transmitted intensity ratio increases by a factor of 8 as the VO2 goes from the semiconductor to the metal phase. We attribute this modulation to the switchable dielectric-permittivity contrast between the air-filled holes in the array and the surrounding VO2 material, a conjecture that is semiquantitatively confirmed by simulation.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
77.22.Ch Permittivity (dielectric function)
42.79.Wc Optical coatings
42.70.-a Optical materials
64.70.K- Solid-solid transitions

Fabrication of integrated nanogap electrodes by surface-catalyzed chemical deposition

Chil Seong Ah, Yong Ju Yun, Joon Sung Lee, Hyung Ju Park, Dong Han Ha, and Wan Soo Yun

Appl. Phys. Lett. 88, 133116 (2006); http://dx.doi.org/10.1063/1.2190464 (3 pages) | Cited 16 times

Online Publication Date: 29 March 2006

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Integrated nanogap electrodes with separations of several nanometers were fabricated by a simple and highly reproducible method of surface-catalyzed chemical deposition. By this method, multifingered nanogap electrodes of a few nanometers in separation were fabricated with a good yield (over 90%). The fabrication was achieved by immersing the initial gap electrodes obtained by conventional e-beam lithography into a stock solution containing Au ions and a mild reducing agent. After the surface-catalyzed chemical deposition, a rather wide initial gap distance of 18–52 nm was decreased to a few nanometers, showing a much narrower distribution (centered at 3.3 nm).
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81.16.Hc Catalytic methods
81.16.Be Chemical synthesis methods
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.46.-w Structure of nanoscale materials
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Angular dependence of silicon oxide etching yield in fluorocarbon chemistries

Ohseung Kwon, Weidong Jin, and Herbert H. Sawin

Appl. Phys. Lett. 88, 133117 (2006); http://dx.doi.org/10.1063/1.2190465 (3 pages) | Cited 1 time

Online Publication Date: 29 March 2006

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High density fluorocarbon plasma for silicon oxide etching has various ion and neutral species. Profile evolution modeling can provide understanding of many difficulties caused by the complexity of the plasma in etching. In this research we have measured etching and deposition rates as functions of ion impinging angle, sample temperature, which are necessary for profile evolution modeling of silicon oxide etching in inductively coupled plasma. Angular dependence of etching yield of oxide in fluorocarbon plasma shows very unique behavior unlike typical ion-induced chemical etching or physical sputtering. Ion-induced deposition model is suggested and tested.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
81.15.Jj Ion and electron beam-assisted deposition; ion plating
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Silicon doped boron carbide nanorod growth via a solid-liquid-solid process

Wei-Qiang Han

Appl. Phys. Lett. 88, 133118 (2006); http://dx.doi.org/10.1063/1.2190468 (3 pages) | Cited 5 times

Online Publication Date: 29 March 2006

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Here we report the synthesis of silicon doped boron carbide (Si-doped B4C) nanorods via a solid reaction using activated carbon, boron, and silicon powder as reactants. These nanorods have been studied by high-resolution transmission electron microscopy, scanning electron microscopy, electron energy loss spectroscopy, and energy-dispersive x-ray spectrometry. The diameter of Si-doped B4C nanorods ranges from 15 to 70 nm. The length of Si-doped B4C nanorods is up to 30 μm. NixCoyBz nanoparticles are used as catalysts for the growth of Si-doped B4C nanorods. A solid-liquid-solid growth mechanism is proposed.
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61.72.up Other materials
81.16.-c Methods of micro- and nanofabrication and processing
68.37.Lp Transmission electron microscopy (TEM)
79.20.Uv Electron energy loss spectroscopy
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Subpicosecond high-power mode locking using flared waveguide monolithic quantum-dot lasers

M. G. Thompson, A. Rae, R. L. Sellin, C. Marinelli, R. V. Penty, I. H. White, A. R. Kovsh, S. S. Mikhrin, D. A. Livshits, and I. L. Krestnikov

Appl. Phys. Lett. 88, 133119 (2006); http://dx.doi.org/10.1063/1.2186110 (3 pages) | Cited 29 times

Online Publication Date: 30 March 2006

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Ultrashort pulse, high-power mode locking is demonstrated in InGaAs quantum dot lasers using a flared waveguide laser incorporating a narrow waveguide sections acting as both a mode filter and saturable absorber. 24 GHz mode locking with 780 fs pulses and 500 mW peak powers are demonstrated at an emissions wavelength of 1.3 μm.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
85.60.-q Optoelectronic devices

Nanobox array for silicon-on-insulator luminescence enhancement at room temperature

B. Cluzel, N. Pauc, V. Calvo, T. Charvolin, and E. Hadji

Appl. Phys. Lett. 88, 133120 (2006); http://dx.doi.org/10.1063/1.2191089 (3 pages) | Cited 4 times

Online Publication Date: 31 March 2006

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We report the light extraction enhancement obtained at room temperature from a square lattice of crystalline silicon nanoboxes etched in a silicon-on-insulator substrate. Luminescence spectra recorded under optical pumping show a 125 times emission enhancement as compared with the reference unpatterned silicon-on-insulator emission. In light of band diagram calculations, it is demonstrated that the emission enhancement partially results from the coupling between electron-hole recombination inside the silicon boxes and low group velocity optical modes of the array. Moreover, it is observed that these modes present different decoupling lengths and that a complete extraction of luminescence can be achieved over less than 15 μm.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.-m Photoluminescence, properties and materials

Long-range-ordered CdTe/GaAs nanodot arrays grown as replicas of nanoporous alumina masks

Mi Jung, Sun-il Mho, and Hong Lee Park

Appl. Phys. Lett. 88, 133121 (2006); http://dx.doi.org/10.1063/1.2191424 (3 pages) | Cited 11 times

Online Publication Date: 31 March 2006

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Long-range-ordered CdTe nanodot arrays with controlled size and density were grown on GaAs substrates by using molecular-beam epitaxy with ultrathin nanoporous alumina masks. The CdTe/GaAs nanodot arrays were grown as replicas of the self-assembled porous alumina masks in spite of the large lattice mismatch between GaAs and CdTe. Using ultrathin alumina masks (ca. 200 nm in thickness), we fabricated CdTe nanodot arrays with uniform dot sizes in the ranges of 35 nm (with a density of ∼ 2.5×1010 cm−2) and 80 nm (with a density of ∼ 8.1×109 cm−2). This is the report on controlling both the size and the density of II-VI/III–V heterostructure semiconductor nanodots.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Formation of ZnO nanoparticles and α-AgI nanocrystals embedded in superionic glass nanocomposites

S. Bhattacharya and A. Ghosh

Appl. Phys. Lett. 88, 133122 (2006); http://dx.doi.org/10.1063/1.2191430 (3 pages) | Cited 2 times

Online Publication Date: 31 March 2006

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We have reported the formation of ZnO nanoparticles and α-AgI nanocrystals embedded in the glass matrix in the 0.70AgI–0.15Ag2O–0.15[xZnO–(1−x)MoO3], x = 0.05–0.30, glass nanocomposites from x-ray diffraction, field emission scanning electron microscopy, and high resolution transmission electron microscopy patterns. Fourier transform infrared spectra have revealed the strong partial covalency due to the presence of Ag+ and MoO42− ions. It is observed that the variation of the conductivity of the composites is well correlated to their structural behavior. A structural model to account for the electrical properties has been proposed.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
72.80.Tm Composite materials
78.30.-j Infrared and Raman spectra
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.46.Hk Nanocrystals

Adjustable pretilt angle of nematic 4-n-pentyl-4′-cyanobiphenyl on self-assembled monolayers formed from organosilanes on square-wave grating silica surfaces

Da-Ren Chiou, Kuan-Yu Yeh, and Li-Jen Chen

Appl. Phys. Lett. 88, 133123 (2006); http://dx.doi.org/10.1063/1.2191472 (3 pages) | Cited 15 times

Online Publication Date: 31 March 2006

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The square-wave grating silica surfaces are fabricated by soft embossing silica sol-gel precursor on glass substrates with an elastomeric polydimethylsiloxane mold. The patterned silica surface could induce the planar alignment of liquid crystal 4-n-pentyl-4′-cyanobiphenyl (5CB) along the direction of microgrooves but with no pretilt angle. The pretilt angle of 5CBs is adjusted from 0° to 90° by the further deposition of organosilane self-assembled monolayers with different functional end-groups on the patterned silica surfaces.
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61.30.-v Liquid crystals

Fiber-content dependency of the optical transparency and thermal expansion of bacterial nanofiber reinforced composites

Masaya Nogi, Shinsuke Ifuku, Kentaro Abe, Keishin Handa, Antonio Norio Nakagaito, and Hiroyuki Yano

Appl. Phys. Lett. 88, 133124 (2006); http://dx.doi.org/10.1063/1.2191667 (3 pages) | Cited 21 times

Online Publication Date: 31 March 2006

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We produced transparent nanocomposite reinforced with bacterial cellulose having a wide range of fiber contents, from 7.4 to 66.1 wt %, by the combination of heat drying and organic solvent exchange methods. The addition of only 7.4 wt % of bacterial cellulose nanofibers, which deteriorated light transmittance by only 2.4%, was able to reduce the coefficient of thermal expansion of acrylic resin from 86×10−6 to 38×10−6 K−1. As such, the nanofiber network of bacterial cellulose has an extraordinary potential as a reinforcement to obtain optically transparent and low thermal expansion materials.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Qk Reinforced polymers and polymer-based composites
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
42.70.-a Optical materials

Stability of strained H:Si(105) and H:Ge(105) surfaces

Cristian V. Ciobanu and Ryan M. Briggs

Appl. Phys. Lett. 88, 133125 (2006); http://dx.doi.org/10.1063/1.2191735 (3 pages) | Cited 3 times

Online Publication Date: 31 March 2006

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We report atomic scale studies of the effect of applied strain and hydrogen environment on the reconstructions of the (105) Si and Ge surfaces. Surface energy calculations for monohydride-terminated (001) and (105) reconstructions reveal that the recently established single-height rebonded model is unstable not only with respect to (001) but also in comparison with other monohydride (105) structures. This finding persists for both Si and Ge, for applied biaxial strains from −4% to 4%, and for nearly the entire relevant domain of the chemical potential of hydrogen, thus providing thermodynamic arguments for the experimentally observed H-induced destabilization of the Ge/Si(105) surface.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Md Surface thermodynamics, surface energies
65.40.G- Other thermodynamical quantities
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